This invention relates to the field of geothermal heating and cooling systems, and more specifically to a geothermal community loop field which serves as a shared means of heat exchange for a plurality of heating and/or cooling loads.
Numerous types of heating and cooling systems are used today as means for controlling the temperature of various thermal loads. Many existing heating and cooling systems, such as heat pumps, air conditioners, and refrigeration units operate on the same thermodynamic principles and utilize the same basic components. Most commonly these basic components include a compressor, an expander, a load heat exchanger, and an external heat exchanger each connected with a piping system which carries a circulating refrigerant throughout the system. This type of heating or cooling system, in order to operate, generally requires a step for heat exchange with the environment. This heat exchange with the environment is typically accomplished by directing the circulating refrigerant to an outdoor coil (i.e., the external heat exchanger) where thermal energy is exchanged between the refrigerant contained in the coils and the outside air.
A significant problem associated with using outside air as the sink or source for a heat exchange process is its inconsistent temperature. For example, a heating system, such as a heat pump operating during the winter, requires the external heat exchanger to absorb thermal energy from the outside air. However, the heating system loses its efficacy and efficiency as the outside temperature falls because less thermal energy can be extracted from the outside air. This problem is compounded due to the fact that as the temperature drops, additional thermal energy is required to heat the load. Similarly, a cooling system, such as an air conditioner, encounters the same efficacy and efficiency problems when the outside temperature rises.
It has previously been recognized that geothermal heat exchange is potentially a more efficient and effective way to perform the external heat exchange required by many heating and cooling systems. Unlike air temperatures, the ground temperature is a relatively constant 65 to 72 degrees F. at a depth below the frost line. Additionally, the ground can act as a virtually limitless energy source or sink.
Geothermal heating and cooling systems are generally comprised of the same essential components as other heating and cooling systems; however, the external heat exchanger operates in a different manner. The external heat exchange process of a geothermal heating or cooling system is generally accomplished by one of two methods. The first method is to simply extend the refrigerant carrying coil into the soil, thereby directly exchanging heat with the ground. The second method utilizes a circulating heat exchange fluid (typically water or an aqueous solution) to carry thermal energy between the ground and the thermal load. Typically, this circulating heat exchange fluid travels in a piping system between a subterranean heat exchanger, where heat is exchanged with the ground, and the thermal load, where heat is exchanged with the heating or cooling system. When the refrigerant carrying coil of the heating or cooling system contacts this circulating heat exchange fluid, heat is exchanged directly with the circulating heat exchange fluid and, thereby, indirectly with the ground.
Most existing large scale residential, commercial, and industrial geothermal heating and cooling systems use a circulating heat exchange fluid to transfer heat between the system and the ground. Heretofore, geothermal systems of this type typically employ a single, dedicated loop field to service each individual thermal load. However, the high initial cost of installing a dedicated loop field for each individual thermal load takes away from the savings provided by more efficient heat exchange. This high initial cost frequently results in a cost recovery period which is longer than what is determined to be economically feasible. Also, when a heating load operates near a cooling load, it is very inefficient for the heating and cooling loads to utilize separate dedicated geothermal loop fields rather than sharing in energy transfer through a single geothermal community loop field.
In the past, a few large scale systems have utilized a shared geothermal community loop field to carry the circulating heat exchange fluid to a plurality of individual thermal loads. However, past systems required that the entire geothermal community loop field be shut down in order to add a new individual thermal load, and after the new unit was added, past systems required the entire loop system to be purged of air before operation could resume. In addition, geothermal community loop fields have not gained widespread use because the high initial cost has been difficult for the loop owner to recover.